# Can a hygromter be calibrated with a regular Boveda humidity pack and zip-lock bag?



## MrBJones (Aug 9, 2015)

Is really necessary to use their calibration kit? They're not at all easy to come by around here...


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## Cigary (Oct 19, 2007)

ONe can use what is called a Salt Test the other a towel test:

The Towel Test:
Dampen a towel (not dripping wet, but good and damp), then wrap the hygrometer in the towel for 30 to 45 minutes. Then unwrap it and read the humidity (quickly). If your hygrometer is perfectly calibrated (few are) it will be reading exactly 100% humidity. Most likely, it will be reading somewhere between 80 and 90%. At this point, whatever the hygrometer reads, you can either set the needle to exactly 100% immediately after the test, or if you're a little lazier, make a mental note of how far over or under the actual humidity is from the reading from your hygrometer.

Try the Salt Test:
Luckily, as nature would have it, when salt and water (NaCl and H2O for you studious types), are in a saturated solution at equilibrium, the resultant humidity is 75%. This gives a fantastic reference point to calibrate our hygrometer. There is an easy way to determine if your hygrometer is accurate. Here's the procedure you should use: you need a ziploc bag, a screw-on beer bottle cap (or other small container) a small amount of salt (regular 'ole table salt), and water.
Place the salt in the bottle cap (or other small container).
Dampen the salt with water. Do not put so much in that the salt gets "sloppy". You want a damp pile of salt in the bottle cap.
Place both the hygrometer and the bottle cap full of damp salt in the ziploc bag and seal it well. (It is important not to let air on or out while the test is going on.)
Keep it like this for over 8 hours.
After 8 hours in the damp salt environment, the actual humidity inside the bag will be 75%. Compare it to your hygrometer, your hygrometer should also read 75%. If not, you will then know exactly how far off your hygrometer is. If it's off, note the amount and direction that it actually reads and be sure to add or subtract that amount when reading the hygrometer. If the hygrometer has a control to adjust it (either the needle or the display), you can set the hygrometer to 75% immediately after the test.


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## MrBJones (Aug 9, 2015)

Thanks for the reply. 

It's a Caliber IV that I'm calibrating. The instructions that came with it say "We recommend the Bovida One-Step Calibration Kit over other testing methods. In no case do we recommend using the salt test. This test is not accurate and can damage and void the warranty on your Caliber IV" (???) Why would that be?


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## CraigT78 (Apr 14, 2015)

MrBJones said:


> Thanks for the reply.
> 
> It's a Caliber IV that I'm calibrating. The instructions that came with it say "We recommend the Bovida One-Step Calibration Kit over other testing methods. In no case do we recommend using the salt test. This test is not accurate and can damage and void the warranty on your Caliber IV" (???) Why would that be?


That's because the salt test, when done at home, is terribly inaccurate. If you do not use the right mixture of salt and water the RH may not be accurate to 75%. In a lab this is controlled, at home it is not. Grab a Boveda pack and your hydrometer in a ziplock and wait 24 hours. Calibrate it to the pack RH. Place it in the zip loc with another Boveda and wait 24 hours. Note the RH. It will likely be within 1%.


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## quazy50 (Aug 6, 2007)

You can use a regular boveda pack but those have a +\- 1% accuracy I believe. The calibration kits (75% or 32%) I think have a +\- .3% or something. You'd be fine using a regular boveda like Craig said. Also, if you want, a calibration kit is relatively cheap on Amazon. 


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## gtechva (Mar 9, 2014)

Without being so specific as to open yourself to stalkers, can you elaborate as to where is "around here"?


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## MrBJones (Aug 9, 2015)

gtechva said:


> Without being so specific as to open yourself to stalkers, can you elaborate as to where is "around here"?


The north Dallas area.


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## Aquaelvis (Jun 23, 2015)

I used salt and then a 65% boveda and didn't notice more than a 1% difference in any of my 5 hygros. Because they don't register fractions of a percent this could be a very slight difference. Even 1% either way is ok with me. I can't imagine lighting up a stick and then throwing it to the ground in disgust because it was stored at 64% and not 65%... Maybe that's just me tho. 
Only reason I could see a company saying not to use it is the corrosive nature of salt or they sell their own brand (or are owned by a company that does) of calibration kit.


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## MrBJones (Aug 9, 2015)

So I bought a Boveda 72 yesterday and last night put it in a ziplock with the Caliber IV. This morning, the Caliber read 71%. Later I noticed it slowly going back and forth between 71 and 72 (but more time at 71). Close enough for the time being. 

Thanks all for responding :vs_smile:


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## quazy50 (Aug 6, 2007)

MrBJones said:


> So I bought a Boveda 72 yesterday and last night put it in a ziplock with the Caliber IV. This morning, the Caliber read 71%. Later I noticed it slowly going back and forth between 71 and 72 (but more time at 71). Close enough for the time being.
> 
> Thanks all for responding :vs_smile:


Ya it'll take about 24 hours to be completely rock solid at what it's reading. You're probably good to go though.

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